Apparatus for fractional sublimation



Feb. 17, 1953 A. F. REID APPARATUS FOR FRACTIONAL SUBLIMATION 2SHEETS-SHEET 1 Filed Jan. 19; 1950 mm vm mm 3 mini mmiuun ,/]NVENTOR.ALLEN F. REID Feb. 17, 1953 FIG.4.

Filed Jan. 19, 1950 FIG.5.

A. F. REID APPARATUS FOR FRACTIONAL SUBLIMATION FIG-7.

2 SHEETSSHEET 2 Has.

INVENTOR. v ALLEN F. REID Patented Feb. 17, 1953 APPARATUS FORFRACTIONAL sosLIMA'rioN Allen Francis iieid Dallas, Tex., assignor tothe United States of America as represented by the United States AtomicEnergy Commission Application January 19, 1950, Serial No. 139,417

Claims. 1

This invention relates to an apparatus for increasing the concentrationof one component in a mixture of diiiicultly separable components, atleast one of which passes from the solid phase into the vapor phasewithout becomin a liquid.

This application is a continuation-in-partof my. co-pending applicationSerial Number 595,191, filed May 21, 1945, now abandoned.

Most of the methods generally used on an industrial scale for separatingthe components of a mixture depend upon someform of liquid-phaseseparation, such as fractional distillation, fractional crystallization,selective extraction and centrifugation. However, none of these methodscan be used efiiciently in separating the components of a solid whichnormally pass directly from the solid to the gaseous phase and which cannot be liquefied at economically practicable temperatures and pressures.The same considerations apply when it is desired'to eiiect a separationbetween a solid and a relatively small quantity of a liquid and thevapor pressures of the solidand the liquid have values that are nearlythe same. Accordingly, it is an object of this invention to provideapparatus for separating difiicultly separable materials, at least oneof which passes directly from the solid phase into the vapor phase. Itis another object of the invention to separate the components of avolatile solid without the use of a liquid-phase process orof a chemicalreaction and to accomplish this object in an essentially simple andwholly practical manner.

A more specific object of the invention is to separate the components ofa volatile solid by progressive fractional sublimation.

:fAnother object of the invention is to provide apparatus for theprogressive sublimation of a volatile solid.

A particular object of the invention is to separate the components of avolatile solid mixture by a process eii'ectively involvingcountercurrent flow of a solid and its vapors.

Still other objects of the invention will be readily inferrable from thedescription following or will be set forth therein.

Generally speaking, the present apparatus is useful in carrying outmethods of separation that involve the alternate condensation andvaporization in alternate heated and cooled zones of a vaporizablemixture having a non-fluid condensed phase, that is, a condensed phasethat is either a solid or a solid-liquid mixture containing so littleliquid that the mixture does not flow under ordinary circumstances. 7One portion of the material vaporized in each heated zone is caused toflow back, countercurrently to the condensed phase, as vaporreflux andbe at least partially condensed in the next preceding-cooled zonewhereas the remainder of the vaporized condensed phase is caused to flowforwardly to the next cooled zone 2 and be at least partially condensedtherein. In the operation of the process, the mixture to be separated,in both condensed and vaporized states, is in motion relative to theseries of alternate hot and cold zones.

One theory of the operation of such processes is presented below withthe understanding that this invention is not limited to any particulartheory and that this discussion is presented only to assist in theunderstandingof the manner in which the invention operates. The mixtureto be separated is admitted to an extended passage which is alternatelyheated and cooled along its length in hot and cold zones which may bemoved relative to th passage (or the passage moved relative to the hotand cold zones). At least a portion of the mixture condenses to a solidin the first cold zone, and any remainder in other cold zones in theseries. The alternate hot and cold zones are then moved relative to thecondensed mixture toward the point wher the mixture was admitted. Hence,the body of the condensed mixture gradually leaves a cold zone andadvances "at the same time into an adjacent hot zone where it isprogressively vaporized, that is, sublimed. The vapor initially formedby this process is enriched with respect to one of the components of themixture because of the difierence in the vaporization rates or thecomponents. Since the vapor pressure in the cold zone will be relativelylow compared to that in the hot zone, a portion of the vapor formed fromthe condensed phase will flow back toward the moving cold zone and berecondensed. This provides what may be termed a vapor reflux. Theremainder of the vapor formed in this hot zone flows towards the nextsucceeding cold zone where it too is condensed. This flow also takesplace because of a diiierence in the pressures between the hot and coldzones. Because the components of the mixture have different rates ofvaporization, difiusion and/or condensation, the mixture condensing inthe second cold zone is enriched in one component relative to themixture remainin in the first cold zone. It should be emphasized thatthere is a zone of relatively high pressure corresponding to each hotzone between a pair of cold zones so that portions of the vapor formedin the hot zone tend to flow both forward and backward through thepassage. achieved primarily because of differences in the rates ofvaporization and condensation and of diffusion among the components ofthe mixture being separated.

' It will be evident that a countercurrent flow of solid and its vaporis achieved in this process. The advantages of such a process aremanifest since many mixtures (including liquid mixtures, as illustratedhereafter) formerly considered to be not readily separable in any simplemanner It is prob-able that the separation is 'may now be easilyseparated by the present process.

Apparatus capable of carrying out the abovedescribed method andembodying th present invention is shown in the accompanying drawings andwill be described in detail hereinbelow. In general, it comprises ahelical passage which is rotatable about its axis together with meansfor establishing in each operative turn of the-helix a hot zone forvaporizing the mixture to be separated and a cold zone for condensingthe vaporized material. Means are also provided for rotating the helixso that condensed material may be mechanically moved relative to the hotand told zones. While the invention will be described with reference toparticular examples of the method and to a particular embodiment of theapparatus it is to be understood that the detailed description is notintended asa limitation on the invention. In the description referencewill be made to the accompanying drawings in which:

Figure 1 is a plan view, largely diagrammatic in character, showing anapparatus embodying the principles of the invention.

Figure'2 is an elevational view of the apparatus shown in Figure 1.

Figure 3 is a sectional view taken on the line 33 of Figure 1 and itshows the manner in which thenhelix is supplied and in which it ismounted on a rotatable shaft.

Figure 4 is a view of the shaft corresponding to the position of theshaft in Figure 2 and parts are in section to show the interiorconstruction of the shaft.

Figure 5 is a plan view of an arm used in supplying material to thehelix and in securing it to the shaft.

Figure 6 is an elevational view of the arm shown in Figure 5. 1

Figure 7 is an end view taken on the line 1-! of Figure l and shows awheel or disk which is mounted on the rotatable shaft and which forms apart of a flexible connection between rotatable and non-rotatableportions of the apparatus.

With reference now to the numerals in the drawings, numeral l indicatesa tubular rotatable shaft supported by the bearings l2 and I3 andadapted to be rotated therein by any suitable driving mechanism (notshown), e. 3-, a gear drive, a chain-and-sprocket or belt-and-pulleydrive. Fixed to one end of the shaft I0 is a fitting I4 that is ineffect an extension of the shaft Ill. The fitting M, as shown in Figure4, has an internal axial bore l6 extending through most of its lengthfrom the free end of the fitting, but not communicating with theinterior of the tubular shaft l0. At the open end of the fitting [4 atube [8 extends into the bore I6 and makes a gas-tight connectiontherewith. The tube I8 in turn communicates with a T-fitting whose arms29 and 22 are provided with valves, designated 24 and 26 respectively.The valves 24 and 26 are used to control the flow of vaporized mixturefrom the raw material containers 28, only one of which is shown, thecontainers being attached by means of the fittings 8B in communicationwith the valve ports. Thus the flow of material from the containers 28passes through valve 24 or 26,

which controls the flow, through the tube l8 into the fitting l4. Gasflows. from th fitting 14 through an opening 39 in thebottom of thefitting, through acut-olf valve 32 and a tube 34 intoa supply arm 36mounted on the shaft [0 for supplying raw material to the helical tube38'. As illustrated best inFigure's and 6, the arm i 36 has an opening40 in which the end of the tube 36 is sealed. The opening 413communicates with an axial passage 42 leading to a second opening 44offset by from the opening 40 and communicating with one end of thehelical tube 38. The shaft l9 engages the arm 36 through a hole 46through one end of the arm. It will be seen that a continuous passage isprovided between the sample containers 28 and z the helical tube 38, thepassage including the fitting l4, tube 34 and the passage 42 in arm 36.

The helical tube 38 is coiled around the shaft l6 as an axis and iseffectively mounted thereon by means of the arm 34 and a second similararm 48 so that it rotates with the shaft. The second arm 48 engages thehelical tube and the shaft [0 at the end of the helical tube oppositethe arm 36. The helical tube 38 therefore communicates through the arm48, which has openlugs and aninternal passage similar to the arm 36,with a tube 59 containing a valve 52. The tube 56 in turn communicatesthrough the arms of a T-fitting 54, whose purpose will be describedpresently, and through a tube 56 with a length of flexible tubing 58that is wound about the surface of a hollow cylinder 59 which is mountedon the shaft H3. The tube 56 extends through the cylinder 59 and issealed into the end of the flexible tubing 58 beyond the end of thecylinder. The end 69 of the flexible tubing 58 remote from the pointwhere it joins the tube 56 is con-' nected through tube 62 with arefrigerated trap 64 for condensibles and through the trap and the tube66 with a vacuum pump 68. Conventional apparatus may be used for boththe trap 64 and the vacuum pump 68. It will be noted at this point thata continuous passage is provided between the helical tube 38 and thevacuum pump 68 through the arm 48, the tubes 50 and 56, the flexibletubing 58 and the refrigerated trap. The flexible tubing 58 is employedto provide a flexible connection between the rigid coil 38 rotatablewith the shaft and the vacu m pump and trap which are not so rotatable.

The cylinder 59, on which the flexible tubing 58 is wound, may bemounted on the shaft I0 for rotation therewith by any suitable means. Asshown in the drawings, the end of the cylinder 59 nearest the helicalcoil 38 is covered by a wheel or disk 70 having screw holes 12therethrough (see Figure 7) and a hole 14 for the tube 56. The disk 16is also provided with a hub 16 by means of which it is mounted on theshaft ill with set screws. The other end of the cylinder 59 ispreferably left open so that the flexible tube 56 may be passed from itspoint of connection with tube 56 through the cylinder and out through anopening '18 cut in the surface of the cylinder. A sealed revolvableconnection between the trap which collects the products obtained fromthe helical coil 38 and the coil itself is therefore provided by thiscombination of cylinder and flexible tubing. In the operation of thedevice the flexible tubing is wound and unwound from the cylinder as theshaft is rotated. Other satisfactory connections could be employed underthe proper circumstances, for example, a bellows seal or ground glassjoints properly mounted. It will be noted that all of the a paratus thathas been described hereinbefore with the exception of the refrigeratedtrap and the vacuum pump is carried by the shaft and all but theflexible tubing, trap" and pump rotate with the shaft. I

the tubular shaft for b-y-passing the helical coil 88. This passagebegins at a second opening 90 in the-fitting M. This openingcommunicates through a tube 92 containing a valve 94 with an opening 96leading to the interior of the tubular shaft I0 which is sealed by a capor plug 88 at the end remote from the fitting M. The interior of theshaft Hi communicates with the flexible tube 58 through the T-fitting 54which is sealed into an opening )0 in the tubular shaft and thencethrough the tube 56. The valves 32 and 52, upstream and downstream ofthe helical tube 38 respectively, may be closed, thus effectivelyisolating the helical tube. This by-pass may be used to evacuate anyatmospheric air which may be admitted to the system while the containers28 are being secured to the fittings 88. During this operation all ofthe valves may be closed but a certain amount of air, for example, willenter thecontainers and/or fittings 88 and the tubes connecting thefittings to the valves 24 and 26.

In order to evacuate these contaminants the valves 32 and 52 are keptclosed while the valve 94 is opened to open the by-pass through the tube9.2, the interior of the tubular shaft, the T 54, the tube 55, and theflexible connector. The vacuum is then applied tothe end of the flexibletube 58 by the vacuum pump 68 and the contaminants are exhausted. Afterthe contaminants have been removed, the valve 94 is closed and thevalves 32 and 52 opened and the separation process' may be carried outas will be presently described in detail.

:As shown in Figure 2, the bottom of the helical coil 38 is refrigeratedto a temperature at which one or both of the components to be separatedare solid by means of a suitable refrigerant contained in a vessel 80,the vessel being diagrammatically illustrated. The upper part of thecoil opposite the refrigerated portion is heated to a temperature atwhich the components to be separated'are vaporized. This may be done byany suitable means such as the hot-gas nozzles 86 used to blow a heatedgas over the coil. Direct heat from a gas flame has also been used butis difficult to control. For many applications an electric radiantheater is to be preferred. Mounted within the coil 38 and generallycoaxial therewith is a cylindrical heat shield 82. The heat shield 82 issecured to and spaced from the coil 38 by means of the spacers 84 whichmay be satisfactorily soldered to the coil and to the shield (see Figure3).

With respect to the materials of construction the apparatus may befabricated of any material that can be used to make the connections andthat will withstand the conditions of operation and the corrosiveproperties of the mixture to be separated. Copper valves and tubing witha helical coil of nickel tubing have been used when handling corrosivefluorides.

The operation of the-apparatus is as follows: A container 28 filled withthe mixture whose components are to be separated is kept in arefrigerated condition to maintain the mixture in the condensed state.The container is attached to one of the fittings 88 mounted on one ofthe valves 24 or 26 with the valve closed. After the container has beensealed on the fitting and contaminant gases exhausted as described, thetemperature of the container is raised to a-value at which its contentsare volatile. The valve to which the container is attached is thenopened flow of the gases into the helical coil is adjusted.

with reference to the number of turns inthe coil- SQ that a portion ofthe mixture condenses ineach refrigerated portion of the coil and sothat the entire quantity of the mixture is condensed within the confinesof the coil. The entire apwise direction when viewed from the valve 52)the more volatile component of the mixturemoves toward the discharge endof the coil to a greater extent than does the less volatile component.That is, the movement of the more volatile component is in the directionof the flexible connector. In this way a separation of the components oran enrichment of the product with respect to one of the components iseffected.

In order to present a more detailed explanation of the operation of theapparatus the theory advanced hereinbefore will be resorted to. However,it will be understood that this explanation merely represents my presentunderstanding of the theory of its operations and that it is notintended to limit the invention to any particular theory of itsoperation. With the helix rotating slowly, the portions of the helicalcoil containing the condensed mixture leave the refrigerant and advancetoward a hot zone. This motion of the coil mechanically transports thecondensed phase toward the warmer zone to vaporize it. This advancedmaterial is vaporized when it reaches the warmer zone, the compositionof the vapor depending upon the relative rates of vaporization of thecomponents of the mixture. Because the pressure in the hot zone of anyturn of the helix is higher than in either the cold zone of the sameturn or of the next, succeeding cold zone in the following turn (byreason of the vapor pressure of the vaporized mixture), 9. portion ofthis vaporized mixture will. flow backward into the cold zone from whichit originated and another portion of the vaporized material will flowforward into the next succeeding cold zone. This lei-directional flow ofvapor may be diffusive or mass flow in nature or some combination ofthese. The vapor flowing in these two directions by reason of the difference in pressure between the hot and the cold zones is condensed whenit reaches the corre-j sponding cold zones. Here the relative rates ofcondensaticnof the components and probably, their relative rates ofdiffusion from the hot; zone will determine the relative concentrationof the material condensing. In View of this bi'-' This process may beconsidered to continue from turn to turn of the helical tube. In thefirst turn of the helix the condensed phase may be said to be subjectedto a progressive sublimation as it is withdrawn from the refrigeratedzone and carried into the heated zone. Incidentally, it is preferablethat the hotand cold zones be as nearly contiguous as possible in orderto prevent mechanical transfer of the condensed phase to a succeedingcold zone. As the material in the form of vapor flows from turn to turnof' the helix it is subjected to repeated progressive sublimations inthe manner described and as a reesultthe material leaving the productend of the helix is relatively rich in the more volatile component. Ananalogy might be drawn between the present method and the operation of arectifying column, there being a succession of vaporcontaining zones andzones containing the condensed phase. In contrast to rectification,however, in the present case, reflux is provided by a flow of vaporrather than by a how of condensed phase.

Before starting a separation run the entire systern should be evacuatedto eliminate so far as is possible gases which do not take part in theseparation. Also, the system should be tested for leaks prior to itsuse. However, the requirements are not so stringent as in high vacuumprocesses, and it is generally sufficiently gastight if the apparatuscan be evacuated to a pressure of less than 1 micron.

A striking example of the utility of this invention is in the separationof perfiuoro-n-heptane (C'zFus) from uranium hexafluoride. A mixture ofthese compounds is formed in certain processes which need not bedetailed here and these mixtures generally contain upwards of 90% UFacontaminated by upwards of 7% CvFie. It is desired to separate the CvFrsand thus to purify the UFs. While the CvFm is a liquid and the UFs asolid at temperatures and pressures of the order of atmospherictemperature and pressure, the actual concentration of the C'lFlS in thismixture is so small that the mixture itself appears to be a solid and isnot wet in a visual or tactile sense. It is therefore not feasible toseparate the liquid from the solid by filtration. Also the CvFu; whichis the contaminant is extremely stable chemically, far more so than theUPS. Chemical means are therefore not practical when it is desired toobtain the UFs.

Moreover, the vapor pressure curves of these two materials are verysimilar and cross each other at a temperature between C. and 10 C., orin other words, at a particular temperature between 0 and 10 C. thevapor pressures of the two components of the mixtures are identical. Athigher temperatures the UFe is the more volatile component while atlower temperatures C7F1c is more volatile. Accordingly, because of thissimilarity in the vapor pressures it is not practicable to separate theliquid from the solid by a conventional drying process. been'foundundesirable to so alter the condi tions of separation as to makepossible a completely liquid-phase separation, e. g., distillation. Aseparation of these components to yield UFs containing no detectableconcentration of C7F1c has been achieved by this invention using theapparatus shown. In carrying out this separation a rotational speed ofone R. P. M. was used with a refrigerant tempertures in the range -10 C.to -40 Cpand a hot gas temperature less than 400 C.

While the particular mixture described contains a liquid component, theprocess is equally successful in separating two or more solids whichpass directly .into the vapor phase.

Thus, in addition to the separation effected between UFs and C'1F1e, thepresent invention has also been used to concentrate mixtures of benzeneand cyclohexane with respect to one of the components. As is well known,these two compounds can be separated only with great difiiculty in theliquid state since their boiling points are about 1 C. apart and theirvapor pressure curves are virtually identical. For example, at C. thevapor pressure of benzene is about 74.9

Again, it has millimeters of mercury while that of cyclohexane at thesame temperature is 76.9 millimeters of mercury. The solid compounds at0 C. have vapor pressures of 24.6 millimeters for benzene and 27.8 forcyclohexane. However, at a temperature of C. the solid compounds havevapor pressures of 2.194 millimeters for benzene and 3.652 millimetersfor cyclohexane. At this temperatur the difference is sufficientlymarked to make feasible an easy separation by means of the presentinvention. The following table is indicative of the degree of separationwhich may be obtained between these two compounds using the presentmethod and apparatus. The speed of rotation in all runs was 0.7 to 0.8R. P. M.

Table I ig g Refrig Hot Volatile Bottoms erant Zone Prod Run No. Mlxt.Percent Percent Temp, Temp, Percent a Com o. "0. can

The advantage gained by using this method and apparatus in effecting aseparation of the type described resides in the fact that the separationmay be carried out at temperatures where the relative vapor pressures ofthe components of the mixture are markedly difierent. As indicatedabove, there is little difference between the vapor pressures of benzeneand cyclohexane even at temperatures as low as 0 C. However, at thetemperatures employed in the foregoing example it will be noted that thevapor pressures of the solids 'difier by as much as or more. Thus thisinvention may be used to separate easily the components of a mixturewhich is normally liquid and .normally very difficult to sepa rate inthe liquid phase. This principle has been applied with some success tothe concentration of the isotope oxygen-lti'using water and to theconcentration of carbon-l4 using a mixture of enriched and normalmesitylene, C6H3(CH3)3. Other mixtures containing or consisting of theisotopic species of an element may similarly b concentrated.

Thus this invention is applicable not only in cases where no liquidphase may be practicably obtained but also in cases where the separationfactor over a practical distillation range is very small but theseparation factor between gas and solid is appreciable. Similarly,mixtures which require that a low temperature be used in handl-ing themmay be easily fractionated without the need of relatively expensive highvacuum equipment. This invention will also find use in cases where theholdup in conventional rectifying columns would be too large to makesuch columns feasible for the purpose, e. ,g., the separation of a smallfraction of a mixture.

In carrying out the process using the apparatus shown in the :drawings,a limited number of revolutions is usually sufficient to produce a verysatisfactory separation. However, this will depend upon. thetemperatures employed and also upon the materials .being separated.

Basically, the separation achieved in this process is effected primarilybecause of the relative thermodynamic properties of the components ofthe mixture. For example, the separation is affected by the differencein the rates of heat transfer between the components of the mixturethemselves and between the components and the heating and cooling meansas well as the relative latent heats of the compounds of the mixture,and their relative rates of condensation and vaporization. It is thoughtalso that the rates of diffusion of the molecules between the hot,high-pressure and cold, low-pressure zones also affects the separation.

The temperature employed on the hot side of the coil is generallydictated by the properties of the materials being separated as well asby the materials of construction. Hence, it is desirable that for eachseparation they be determined empirically. The pressure within theapparatus is determined primarily by the temperature in the cold zone ofthe tube and is generally close I to the vapor pressure of the condensedphase at that temperature. The} rate of rotation depends not only on therelative concentrations of the components of the mixture but also on thenum ber of turns in the coil and on the desired degree of purity ofproduct.

In addition to the separation of UFs from CqFm the process may also beused to separate UFs from perfluoro-dimethyl-cyclohexane (CBFIG) or fromhydrogen fluoride (HF). Similarly, either CvFw or CsFm may be separatedfrom hydrogen fluoride by this method. Many other alternatives in theprocess variables and in the elements of the apparatus will be apparentto those skilled in the art as will be many other applications of thisinvention.

Since many embodiments might be made of the present invention and sincemany changes might be made in the embodiment described, it is to beunderstood that the foregoing description is to be interpreted asillustrative only and not in a limiting sense.

I claim:

1. In apparatus for separating the components of a difilcultlyseparable, .vaporizable mixture, in combination, a tube wound in theform of a helix and rotatable about the axis of said helix, means forintroducing said mixture into said tube, means longitudinally disposedto the axis of said helix for establishing in corresponding portions ofeach operative turn of said tube a zone of relatively low temperatureadapted to condense said mixture, separate means longitudinally disposedwith respect to the axis of said helix for establishing in each saidoperative turn of said tube a zone of relatively high temperatureadapted to vaporize said mixture, said condensing and vaporizing meansbeing spaced circumferentially about said helix and extendinglongitudinally thereof, and means for rotating said tube.

2. In apparatus for separating the components of a difiicultlyseparable, vaporizable mixture, in combination, a tube in the form of ahelix adapted to be rotated about the axis of said helix, means forintroducing said mixture into said tube, heating means longitudinallydisposed with respect to the axis of said helix and adapted to heatcorresponding portions of each operative turn of said tube to avaporization temperature of said mixture. separate refrigerating meanslongitudinally disposed to the axis of said helix densing temperature ofsaid mixture, said heating and refrigerating means extendinglongitudinally of said helix and being spaced circumferentiallythereabout, and means for rotating said tube.

3. Apparatus according to claim 2 in which both the heating means andthe refrigerating means are positioned outside the helix and in which aheat-reflecting member is mounted within the helix and is adapted toreflect heat from the heating means to the inner surfaces of thecorresponding portions of the operative turns of the tube.

4. In apparatus for separating the components of a diiiicultlyseparable, vaporizable mixture, in combination, a tube in the form of ahelix r0- tatable about the axis of the helix. means for introducingsaid mixture into said tube, heating means longitudinally disposed withrespect to the axis of said helix, said heating means being adapted toheat corresponding portions of'each operative turn of said tube to avaporizing temperature of said mixture, separate refrigerating meanslongitudinally disposed with respect to the axis of said helix andincluding a cooling medium in contact with corresponding portions ofeach said operative turn of said tube adapted to cool said mixture toits condensing temperature, said heating and refrigerating means beingspaced circumferentially about said helix and extending longitudinallythereof, and means for rotating said tube.

5. In apparatus for separating the components of a difficultlyseparable, vaporizable mixture, in combination, a tube in the form of ahelix having a horizontal axis and being rotatable thereabout, means forintroducing said mixture into said tube, a heater positioned above saidtube and adapted to heat the upper portion of each turn of said tube toa vaporizing temperature of said mixture, said heater beinglongitudinally disposed with respect to the axis of said helix, a

separate refrigerator positioned below saidtube and including arefrigerant in which the lower portion of each turn of said tube isimmersed, said refrigerant being adapted to cool said mixture to itscondensing temperature, said refrigerator being longitudinally disposedwith respect to the axis of said helix, said heater and refrig eratorbeing spaced circumferentially about said helix and extendinglongitudinally thereof, a cylindrical heat-reflecting member mountedaxially Within said helix to reflect heat from said heater to the innersurfaces of each said turn of said tube, and means for rotating saidtube.

ALLEN FRANCIS REID.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,589,373 De Remer June 22, 1926FOREIGN PATENTS Number Country Date 5,315 Great Britain June 27, 182687,654 Switzerland Jan. 3, 1921

1. IN APPARATUS FOR SEPARATING THE COMPONENTS OF A DIFFICULTY SEPARABLE,VAPORIZABLE MIXTURE, IN COMBINATION, A TUBE WOUND IN THE FORM OF A HELIXAND ROTATABLE ABOUT THE AXIS OF SAID HELIX, MEANS FOR INTRODUCING SAIDMIXTURE INTO SAID TUBE, MEANS LONGITUDINALLY DISPOSED TO THE AXIS OFSAID HELIX FOR ESTABLISHING IN CORRESPONDING PORTIONS OF EACH OPERATIVETURN OF SAID TUBE A ZONE OF RELATIVELY LOW TEMPERATURE ADAPTED TOCONDENSE SAID MIXTURE, SEPARATE MEANS LONGITUDINALLY DISPOSED WITHRESPECT TO THE AXIS OF SAID HELIX FOR ESTABLISHING IN EACH SAIDOPERATIVE TURN OF SAID TUBE A ZONE OF RELATIVELY HIGH TEMERATURE ADAPTEDTO VAPORIZE SAID MIXTURE, SAID CONDENSING AND VAPORIZING MEANS BEINGSPACED CIRCUMFERENTIALLY ABOUT SAID HELIX AND EXTENDING LONGITUDINALLYTHEREOF, AND MEANS FOR ROTATING SAID TUBE.